Prestressed concrete tank, process and structural unit therefor



T THEREFOR Oct. 25, 1966 F. x. CROWLEY PRESTRESSED CONCRETE TANK, PROCESS AND STRUCTURAL UNI Filed July 6, 1962 INVENTOR CA.

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wgw via/(w? United States Patent 3,280,525 PRESTRESSED CONCRETE TANK, PROCESS AND STRUCTURAL UNIT THEREFOR Francis X. Crowley, Brookline, Mass, assignor to Crowley Hessian Engineers, Boston, Mass., a partnership Filed July 6, 1962, Ser. No. 207,898 4 Claims. (Cl. 5222 This invention comprises a concrete tank of a new and improved structure which makes it possible to assemble the tank on the site from precast concrete units and then subject it as an integrated assembly to prestressing. The invention also includes Within its scope the structural unit herein disclosed as an element of the tank, as well as the novel process of erecting the tank.

Heretofore prestressed concrete tanks have been erected from the ground up at the site and the work has been subjected to all the annoyance and delay of inclement weather, delayed transportation of raw material, inavailability of labor, etc.

The present invention makes it possible for the first time to bring to the site precast concrete units which have been purshased by the contractor or fabricated by him at convenient time and place, as for example, during the Winter at his own headquarters.

These units are characterized by sheet metal sheathing permanently bonded to one face of a precast concrete panel and presenting parallel longitudinal undercut channels. The units may be conveniently formed of hydraulic concrete deposited upon a sheet steel diaphragm in which the channels have been already formed, the panels being of a length commensurate with the height of the contemplated tank. The diaphragm is formed with a half channel at either edge of the panel, the complete channel being formed with a half chanel of the adjacent panel and the complete channel being shaped to receive an elongated locking key plate which locks the panels together as an integrated assembly adapted for prestressing by an encircling wire.

The longitudinal channels formed in the metal sheathing may be undercut or formed with opposed reentrant angular walls so that the channel is wider at the bottom than at its open outer side. It is thus adapted to receive a metal key plate of the same general cross section. This may be inserted lengthwise in the channel or forced resiliently into place, and in association with a sealing layer or coating of elastomeric material which cooperates with the key plate to form a sealed fluid-tight joint. The panels assembled as a cylinder upon the foundation present longitudinal channels between their adjacent edges. These are filled with mortar and the cylinder is encased with pneumatically projected mortar forming an outer coating or wall which may be varied in thickness from top to botom, thus conforming to the structural requirements of the tank and facilitate the formation of a water seal with the foundation. This wall is of course formed at the site of the tank and without the necessity of employing forms.

These and other features and advantages of the invention will be best understood and appreciated from the following description of a preferred embodiment thereof, selected for purposes of illustration and shown in the accompanying drawings, in which:

FIG. 1 is a cross sectional View of portions of assembled panels,

FIG. 2 is a view in elevation of a complete panel, shown with a portion broken away, and

FIG. 3 is a fragmentary view in longitudinal section on the line 3-3 of FIG. 1.

The structural units of which the tank is composed have a precast body 11 of concrete, herein shown as sheathed upon its outer face with sheet steel 12, or it may be other sheet metal. The body 11 is formed on the sheathing with parallel longitudinal undercut channels 13 having opposed reentrant angular walls that make the channel wider at its close-d inner wall than at its outer open side. At each side edge the body 11 is formed in a half channel 13' so that when assembled the half channels of adjacent units form together a complete common undercut channel.

The sheathing for each unit is erected or laid out as part of a mold diaphragm and the concrete body 11 is now precast upon it, preferably by deposting hydraulic cement thereon. In this step the concrete surrounds the projecting dovetail ribs on the inner face of the sheathing and becomes permanently bonded thereto. The sheathing is folded along each edge 14 to provide a reinforced contact and gauge edge for determining the correct assembled relation of the units as indicated in FIG. 1. The folded edge of the sheathing is embedded in the concrete body 11 so that no raw edge of metal is exposed at the longitudinal edges of the unit.

The edge walls 15 of the concrete body are given a clearance angle such that they define open spaces or channels between the assembled units when their contact edges meet. These spaces are filled in a subsequent constructional step with hydraulic mortar 16 or other suitable cementitious grouting.

The units thus constructed by be commensurate in length with the height of the contemplated tank, for example 20 to 40 feet or more, 6 to 8 feet in width and 3 to 12 inches in thickness. They are thus portable and may be transported to and stacked at the site of the tank in readiness for assembling and erected at the contractors convenience.

At the selected site a solid foundation 23 is first constructed and upon this the sheathed panel units are erected in circular or polygonal assembly with their contact edges engaged as shown in FIG. 1. The half channels in the steel sheathing are brought into cooperative relation so that the whole external surface of the sheathing presents a series of equally spaced vertical undercut channels. The units are now locked together in flush relation by the insertion of a metal key plates 24 which are similar in cross section to that of the channels but just enough smaller to fit snugly when forcibly driven in place from the top of the structure thus forming with the metal sheath-ing 12 a complete metal enclosure of the tank.

The layer or gasket 25 of any suitable elastomeric sealing compound may be inserted beneath the key plates 24 in each common channel thus forming a fluid-tight joint between the side walls of adjacent sections.

Having completed the erection and connection of the panels as above explained an intermediate wall 17 of cement is 'formed upon the outer facing of the ribbed sheathing 12. This may be formed of cement pneumatically projected by the Gunite process or any casting procedure. The tank at this stage in its construction is prestressed by wires 18 wound under high tension upon the surface of the intermediate wall 17. In this way the tank as a whole is maintained always under compression regardless of the level of its contents.

After the prestressed step an outer or cover wall 19 is applied over the wire 18 and bonded to the intermediate wall 17. This wall may be shaped as desired and is herein shown as having an outwardly bulged foot section 20 which imparts stability and improves the appearance of the tank structure. The lower turns of the prestressing wire may be put in place as the foot section 20 is being built up.

The entire wall of the tank may be supported on blocks or segments 21 of rubber or other elastomer and a fluidtight seal between the wall 11 and the base 23 is insured by a molded ring 22 of rubber or other elastomer which is embedded in the foundation and the foot of the intermediate wall 17 when these elements are constructed at the side of the tank. In this way the wall of the tank is given the freedom of movement that may be required to compensate for expansion or contraction due to variations of temperature or prestressing without impairing the integrity of the seal.

The inwardly opening channels between the present bodies 11 of the units may be filled with cementitious mortar 16 at any convenient stage before the prestressing of the tank, as for example, during or after the formation of the intermediate wall 17. The presence of this filler is necessary in order to transmit the prestressing force from one panel to another.

The locking plates 24 may be of rigid construction or they may be sufficiently resilient to be forced or driven into locking position in the channels of the sheathing.

The narrower the individual units are the less is the shearing stress to which they are subjected, and under all conditions shearing stress is dissipated at the joints which include the filler 16.

Having thus disclosed my invention and described an illustrative procedure for carrying it out, I claim as new and desire to secure by Letters Patent:

1. A prestressed concrete tank having a core wall comprising elongated panels of precast concrete having on one face a sheet of sheet metal presenting longitudinal channels, the said panels being assembled side-by-side and united by elongated key plates of steel fitted into the channels of adjacent units and forming with the sheet metal sheathing of the panels a complete metallic enclosure for the tank, an intermediate coating of cement enclosing the assembled panels, prestressing wires wound under tension upon said coating, and a surface coating of cement enclosing the prestressing wires.

2. A prestressed concrete tank as defined in claim 1, further characterized in that the longitudinal channels in the sheathing of the panels are reentrant and undercut and the elongated metal key plates are sufiiciently resilient to be sprung into said channels and to hold the panels in flush relation and edge to edge contact.

3. A prestressed concrete tank having a core wall comprising elongated panels of concrete precast with an outer metallic sheath of sheet metal presenting parallel external channels with opposed reentrant angular Walls, the said panels being assembled side by side and interlocked in flush relation and edgewise contact by elongated strips of sheet metal fitted into channels of adjacent units together with enclosed elastomeric sealing compound, a coating of hydraulic mortar enclosing the metallic sheaths of the assembled panels, prestressing wires located under tension upon said coating, thus subjecting the assembled panels to edgewise compression, and a surface coating of hydraulic mortar imparting a smooth finish to the tank as a whole.

4. The process of erecting and prestressing a concrete tank comprising the steps of assembling in cylindrical formation a series of panels of concrete precast with metal sheathing which presents undercut longitudinal edge channels, interlocking the assembled units by driving metal key plates in the adjacent channels, thus forming a complete metallic enclosure for the tank and locking the panels in flush relation and edge to edge contact, prestressing the interlocked units as an integrated assembly; and providing the prestressed assembly with a cover coat of hydraulic concrete.

References Cited by the Examiner UNITED STATES PATENTS 720,831 2/1903 Mauntin 52471 910,757 1/1909 Wilson 52336 932,367 8/1909 Bassford 52459 954,814 4/ 1910 Lawrence 52378 1,735,447 11/1929 Zaisser 52417 1,792,491 2/ 1931 Goldsmith 52411 1,892,498 12/1932 Adams 52411 2,074,592 3/ 1937 Rowell 52224 2,075,872 4/1937 Smith 52248 2,140,226 12/ 1938 Harrap 52396 2,204,955 6/ 1940 Beeby 52224 2,370,780 3/ 1945 Crorn 5 2224 2,418,580 4/ 1947 Crom 52249 2,932,964 4/1960 Dobell 52224 3,119,153 1/1964 Martin 5282 OTHER REFERENCES Doanides, Peter 1.: Big Prestressed Concrete Tanks Built With Precast Panels. In Civil Engineering Mag. 25 (9), pages 44-46, September 1955, TA l.c61.

FRANK L. ABBOTT, Primary Examiner.

JACOB L. NACKENOFF, EARL J. WITMER,

Examiners.

R. A. STENZEL, Assistant Examiner. 

1. A PRESTRESSED CONCRETE TANK HAVING A CORE WALL COMPRISING ELONGATED PANELS OF PRECAST CONCRETE HAVING ON ONE FACE A SHEET OF SHEET METAL PRESENTING LONGITUDINAL CHANNELS, THE SAID PANELS BEING ASSEMBLED SIDE-BY-SIDE AND UNITED BY ELONGATED KEY PLATES OF STEEL FITTED INTO THE CHANNELS OF ADJACENT UNITS AND FORMING WITH THE SHEET METAL SHEATHING OF THE PANELS A COMPLETE METALLIC EN- 